Transcript CH 9 PowerPoint

How Cells Harvest Energy
Chapter 9 Outline
•Cellular Energy Harvest
•Cellular Respiration
–Glycolysis
–Oxidation of Pyruvate
–Krebs Cycle
–Electron Transport Chain
•Catabolism of Protein and Fat
•Fermentation
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Cellular Respiration
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Cells harvest energy by breaking bonds and
shifting electrons from one molecule to
another.
– aerobic respiration - final electron acceptor
is oxygen
– anaerobic respiration - final electron
acceptor is inorganic molecule other than
oxygen
– fermentation - final electron acceptor is an
organic molecule
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ATP
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Adenosine Triphosphate (ATP) is the energy
currency of the cell.
– used to drive movement
– used to drive endergonic reactions
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ATP
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Most of the ATP produced in cells is made by
the enzyme ATP synthase.
– Enzyme is embedded in the membrane
and provides a channel through which
protons can cross the membrane down
their concentration gradient.
 ATP synthesis is achieved by a rotary
motor driven by a gradient of protons.
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NAD+ & NADH
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Nicotinamide adenine dinucleotide, NAD+, is a
coenzyme found in all living cells.
The compound is a dinucleotide, since it consists of two
nucleotides joined through their phosphate groups: with one
nucleotide containing an adenosine ring, and the other
containing nicotinamide.
In metabolism, NAD+ is involved in redox reactions,
carrying electrons from one reaction to another.
The coenzyme is therefore found in two forms in cells:
NAD+ is an oxidizing agent – it accepts electrons from
other molecules and becomes reduced,
this reaction forms NADH, which can then be used as a
reducing agent to donate electrons. These electron transfer
reactions are the main function of NAD+.
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NAD+ & NADH
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The Cellular isms
Metabolism: is the set of chemical
reactions that occur in living organisms in
order to maintain life.
– These processes allow organisms to grow
and reproduce, maintain their structures,
and respond to their environments.
– Usually divided into two categories.
Catabolism and Anabolism
Catabolism – breaking down
Anabolism – building up
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The Cellular isms
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Catabolism: the set of metabolic pathways
which break down molecules into smaller
units and release energy.
– Large molecules such as polysaccharides,
lipids, nucleic acids and proteins are
broken down into smaller units such as
monosaccharides, fatty acids, nucleotides
and amino acids, respectively.
– These processes produce energy
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The Cellular isms
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Anabolism: the set of metabolic pathways that
construct molecules from smaller units.
– These reactions require energy.
– Anabolism is powered by catabolism. Many
anabolic processes are powered by adenosine
triphosphate (ATP).
– Anabolic processes tend toward "building up"
organs and tissues.
– These processes produce growth and
differentiation of cells and increase in body size,
a process that involves synthesis of complex
molecules.
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Glucose Catabolism
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Cells catabolize organic molecules and
produce ATP in two ways:
– substrate-level phosphorylation
– aerobic respiration
 in most organisms, both are combined
 glycolysis
 pyruvate oxidation
 Krebs cycle
 electron transport chain
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Aerobic Respiration
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Stage One - Glycolysis
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For each molecule of glucose that passes
through glycolysis, the cell nets two ATP
molecules.
Priming
– glucose priming
– cleavage and rearrangement
Substrate-level phosphorylation
– oxidation
– ATP generation
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Priming Reactions
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Cleavage Reactions
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Energy-Harvesting Reactions
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Recycling NADH
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As long as food molecules are available to
be converted into glucose, a cell can
produce ATP.
– Continual production creates NADH
accumulation and NAD+ depletion.
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 NADH must be recycled into NAD .
 aerobic respiration
 fermentation
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Recycling NADH
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Stage Two - Oxidation of Pyruvate
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Within mitochondria, pyruvate is
decarboxylated, yielding acetyl-CoA, NADH,
and CO2.
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Stage Three - Krebs Cycle
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Acetyl-CoA is oxidized in a series of nine
reactions.
– two steps:
 priming
 energy extraction
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Overview of Krebs Cycle
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1: Condensation
2-3: Isomerization
4: First oxidation
5: Second oxidation
6: Substrate-level phosphorylation
7: Third oxidation
8-9: Regeneration and oxaloacetate
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Krebs Cycle
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Krebs Cycle
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Harvesting Energy by Extracting Electrons
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Glucose catabolism involves a series of
oxidation-reduction reactions that release
energy by repositioning electrons closer to
oxygen atoms.
– Energy is harvested from glucose
molecules in gradual steps, using NAD+ as
an electron carrier.
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Electron Transport
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Stage Four: The Electron Transport Chain
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NADH molecules carry electrons to the inner
mitochondrial membrane, where they
transfer electrons to a series of membraneassociated proteins.
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Electron Transport Chain
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Chemiosmosis
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ATP Generation
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This process begins with pyruvate, the product of
glycolysis, and ends with the synthesis of ATP
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Theoretical ATP Yield of Aerobic Respiration
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Regulating Aerobic Respiration
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Control of glucose catabolism occurs at two
key points in the catabolic pathway.
– glycolysis - phosphofructokinase
– Krebs cycle - citrate synthetase
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Control of Glucose Catabolism
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Catabolism of Proteins and Fats
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Proteins are utilized by deaminating their
amino acids, and then metabolizing the
product.
Fats are utilized by beta-oxidation.
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Cellular Extraction of Chemical Energy
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Fermentation
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Electrons that result from the glycolytic
breakdown of glucose are donated to an
organic molecule.
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– regenerates NAD from NADH
 ethanol fermentation
 lactic acid fermentation
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